1. Field of the Invention
The present invention relates to a disk drive apparatus equipped with disks on which servo information is prestored at regular intervals in the direction of the circumference of the disk, and more particularly to a disk drive apparatus and method for detecting a servo mark contained in the servo information and used to identify it, thereby generating a servo sector pulse.
2. Description of the Related Art
A hard disk drive is known as a disk drive using disks as storage mediums. In the hard disk drive, a head positioning control is executed in which a head is moved to a target track and is then positioned in a target area on the target track. Head positioning control is generally executed on the basis of servo information discretely recorded on each disk at regular intervals in the direction of the circumference of each disk. Further, head positioning control is executed during an interrupt process executed by a CPU. The interrupt process is executed in accordance with a servo sector pulse. The servo sector pulse is generated in accordance with the detection of a servo mark contained in the servo information and used to identify it.
To generate the servo sector pulse, two types of generating methods as described in Jpn. Pat. Appln. KOKAI Publication No. 8-31102 are used. In the first servo-sector-pulse-generating method, a particular pattern for generating a servo sector pulse, i.e., a servo mark for identifying servo information, is detected. The particular pattern or servo mark is contained in servo information recorded on each of the servo areas (servo sectors) that are discretely arranged at regular intervals on each disk in the direction of the circumference of each disk. Each time a servo mark is detected, a servo sector pulse is generated at a time point (first timing) a predetermined time period T1 after the detection time of the servo mark. In the second servo-sector-pulse-generating method, the servo sector pulse is generated at a time point (second timing) a predetermined time period T2 (T2>>T1) after the detection time of a preceding servo mark. To measure the time period T2, a timer is used. When the first and second servo-sector-pulse-generating methods are used, even if the detection of a servo mark has failed due to, for example, noise, the failure can be compensated for by generating a pseudo servo sector pulse the predetermined time period T2 after the detection time of a preceding servo mark.
As described above, in the prior art, when a servo mark contained in servo information is detected, a servo sector pulse is generated at the first timing the predetermined time period T1 after the detection. Further, when the detection of a servo mark has failed for some reason, a servo sector pulse is generated at the second timing the predetermined time period T2 after the detection of a servo mark from servo information recorded in a preceding servo area. Thus, the failure of generation of a servo sector pulse due to the failure of detection of a servo mark can be compensated for.
However, in the prior art, no consideration is given to the fact that the intervals at which servo information is detected, i.e., the servo intervals, vary according to changes in the rotational speed of a disk, i.e., a motor for spinning the disk, or runout of the disk, i.e., runout of the motor shaft. Accordingly, in the prior art, the predetermined time period T2 is always used as the timing (second timing) for generating a pseudo servo sector pulse when the detection of a servo mark has failed.
Therefore, in the prior art, if the servo intervals exceed the time period T2, it is determined that the detection of a servo mark has failed, thereby generating a servo sector pulse at the second timing the predetermined time period T2 after the detection of a preceding servo mark. Accordingly, if the servo intervals vary due to changes in the rotational speed of a disk or runout of the disk, it is possible that two servo sector pulses will be generated at different time points for one servo information item corresponding to one servo area.